1. Field of the Invention
The present invention relates to an aromatic vinyl polymer resin composition and its moldings. More precisely, the invention relates to an aromatic vinyl polymer resin composition suitable to molding into resin foam sheets having a good appearance well balanced with the mechanical strength thereof even when the expansion ratio in molding is increased, and to its resin foam sheets and containers.
2. Description of the Related Art
Aromatic vinyl polymer resin, especially atactic polystyrene resin is a plastic material inexpensive and having the advantages of good extrudability, injection moldability and fabricability, and it has many applications, for example, for electric appliances for household use, implements for office use and food wrapping and packaging materials. In particular, since resin foam sheets and moldings of such aromatic vinyl polymer resin are easy to fabricate and are tough and have good heat-retaining properties, they are indispensable in the field of food wrapping and packaging technology.
However, the resin foam sheets and moldings have a problem in that their surface smoothness and glossiness may lower and lose a feel of high-quality appearance with the increase in their expansion ratio. The problem of poor surface condition of the sheets and moldings leads to another problem when they are directly printed with ink in a mode of profile printing, in that the appearance of their printed surfaces is extremely bad.
To solve the problems with the resin foam sheets and moldings, in general, the expansion ratio of the aromatic vinyl polymer resin for them is controlled to fall in a low range of from 1.5 to 2.5 times to thereby make them have a feel of high-quality appearance. For the moldings having the resin expansion ratio of from 3 to 12 times, applied is a method of laminating their surface with a non-foam film, and the film-laminated moldings are printed on the film in a mode of profile printing. However, the method of controlling the expansion ratio in molding the resin and the method of laminating the moldings with a non-foam film increase the production costs. Therefore, it is desired to develop an inexpensive method of molding the resin into foam sheets or moldings having good surface smoothness and glossiness even when the resin expansion ratio is high.